Obesity, and especially upper body obesity, is a common and very serious public health problem in the United States and throughout the world. According to recent statistics, more than 25% of the United States population and 27% of the Canadian population are over weight. Kuczmarski, Amer. J. of Clin. Nut. 55: 495S-502S (1992); Reeder et. al., Can. Med. Ass. J., 23:226-233 (1992). Upper body obesity is the strongest risk factor known for type II diabetes mellitus, and is a strong risk factor for cardiovascular disease and cancer as well. Recent estimates for the medical cost of obesity are $150,000,000,000 world wide. The problem has become serious enough that the surgeon general has begun an initiative to combat the ever increasing adiposity rampant in American society.
Much of this obesity induced pathology can be attributed to the strong association with dyslipidemia, hypertension, and insulin resistance. Many studies have demonstrated that reduction in obesity by diet and exercise reduces these risk factors dramatically. Unfortunately these treatments are largely unsuccessful with a failure rate reaching 95%. This failure may be due to the fact that the condition is strongly associated with genetically inherited factors that contribute to increased appetite, preference for highly caloric foods, reduced physical activity, and increased lipogenic metabolism. This indicates that people inheriting these genetic traits are prone to becoming obese regardless of their efforts to combat the condition. Therefore, a new pharmacological agent that can correct this adiposity handicap and allow the physician to successfully treat obese patients in spite of their genetic inheritance is needed.
The ob/ob mouse is a model of obesity and diabetes that is known to carry an autosomal recessive trait linked to a mutation in the sixth chromosome. Recently, Yiying Zhang and co-workers published the positional cloning of the mouse gene linked with this condition. Yiying Zhang et al. Nature 372: 425-32 (1994). This report disclosed a gene coding for a 167 amino acid protein with a 21 amino acid signal peptide that is exclusively expressed in adipose tissue. The report continues to disclose that a mutation resulting in the conversion of a codon for arginine at position 105 to a stop codon results in the expression of a truncated protein, which presumably is inactive.
Physiologist have postulated for years that, when a mammal overeats, the resulting excess fat signals to the brain that the body is obese which, in turn, causes the body to eat less and burn more fuel. G. R. Harvey, Nature 227: 629-631 (1969). This "feedback" model is supported by parabiotic experiments, which implicate a circulating hormone controlling adiposity. Based on this model, the protein, which is apparently encoded by the ob gene, is now speculated to be an adiposity regulating hormone.
Pharmacological agents which are biologically active and mimic the activity of this protein are useful to help patients regulate their appetite and metabolism and thereby control their adiposity. Until the present invention, such a pharmacological agent was unknown.
The present invention provides biologically active anti-obesity proteins. Such agents therefore allow patients to overcome their obesity handicap and live normal lives with a more normalized risk for type II diabetes, cardiovascular disease and cancer.